Liverpool were clinical as Mohamed Salah added a third early in the second half to make it three wins out of three for Slot, but this was a second defeat of the young season for a poor United side, and Ten Hag cut a frustrated figure on the Old Trafford touchline.

The issues that dogged United for much of last season and the start of this were ruthlessly exposed as Liverpool cut through United's midfield time and again. Casemiro, at fault for two of the goals, was hauled off at half-time but little changed, with Liverpool better in every department.

Slot had already enjoyed a 3-0 pre-season friendly victory over United in the summer but this win saw him become the first Liverpool boss to beat United in his first competitive meeting since Bob Paisley in 1975.

There was an early warning sign when Liverpool had a goal awarded by one form of technology only to be ruled out by another just six minutes in.

Referee Anthony Taylor pointed to his watch to indicate Trent Alexander-Arnold's shot had crossed the line before striking Diogo Dalot and bouncing clear, but VAR John Brooks then intervened as Salah was offside when he knocked Diaz's low ball into Alexander-Arnold's path.

It was a let-off for United given the ease with which Ryan Gravenberch had carved through their midfield to create the opportunity. Ten Hag's side tried to settle the game down, controlling the tempo for a period, but doing so at the expense of offering any threat themselves.

Liverpool were happy to keep probing, and their reward came in the 35th minute.

Casemiro needlessly passed straight to Gravenberch, who once again found the space to charge forward before slipping the ball wide to Salah, and the only challenge to Diaz looking to head in at the far post was his own team-mate Dominik Szoboszlai, who ducked out of the way.

United soon had a chance to hit back when Bruno Fernandes' cross was deflected into the path of Noussair Mazraoui. His low shot fizzed through the legs of Virgil van Dijk but the unsighted Alisson Becker did enough to scramble it clear.

Instead Liverpool doubled their lead three minutes before half-time, with Casemiro again involved for the wrong reasons.

Diaz picked his pocket in midfield, and while United looked to Taylor in vain for a free-kick, Diaz swapped passes with Salah before turning a low shot inside the post.

Toby Collyer replaced Casemiro at the break and the 20-year-old was quickly involved in setting up a chance for Joshua Zirkzee, whose shot was pushed wide by Alisson.

But although Casemiro had gone Liverpool were still bossing the midfield, and after Alexis Mac Allister dispossessed Kobbie Mainoo, Szoboszlai teed up Salah to make it three in a swift counter in the 56th minute.

United were on the rocks, and Salah almost added a fourth a couple of minutes later, denied by Andre Onana, while Cody Gakpo headed narrowly wide from Szoboszlai's cross moments after coming on.

United offered some late threat. Zirkzee should have done better with a close-range header but directed it straight at Alisson, before defender Lisandro Martinez tried an unlikely overhead kick from substitute Amad Diallo's cross, but missed the target.

Zirkzee then missed another chance, unable to get his shot on target as he met Dalot's cross at the far post, but Ten Hag's side were well beaten.

Luis Diaz brace sees Liverpool overturn Manchester United at Old Trafford